Here is the full list of all 18 Reverse Crawl achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Unlock the Iron Golem power
The easiest choice to make
Achieve either of the good endings
Unlocked the Horned Demon power
Complete two Sage quests in one campaign
Complete two Merchant quests in one campaign
The hardest choice to make
Achieve the evil ending
Collect all three of Greybeard's books in one campaign
Unlock the Red Dragon power
Complete two Hero Party quests in one campaign
The cruellest choice to make
Complete Chapter 7
Recruit Greybeard the Exiled Mage
Recruit Violet the Dark Elf
Defeat a hero
Trigger an Evil Power
Recruit Bonehead the Goblin Shaman